Lower alkyl esters of 6, 7-di (lower) alkoxy-4-hydroxy-3-quinolinecarboxylic acid



United States Patent 3,267,166 LOWER ALKYL TESTERS 0F 6,7-DI(LOWER) ALKOXY- i-HYDRQXY 3 -QU1NOLINECAR- BGXYLIC ACID Edward John Watson, FL, Norwich, N.Y., assignor to The Nor wieh Pharmacal Company, Norwich, N.Y., a corporation of New York No Drawing. Filed July 2, 1964, Ser. No. 380,058 9 Claims. (Cl. 260-287) This application is a continuation-in-part of my copending application Serial No. 272,858, filed April 11, 1963, now abandoned, which, in turn, is a continuationin-part of my application Serial No. 242,933, filed December 7, 1962, now abandoned, which, in turn, is a continuation-in-part of my application Serial No. 185,806, filed April 9, 1962, now abandoned; and is filed as a substitute therefor.

This invention relates to new chemical compounds, lower alkyl esters of 6,7-di(lower)alkoxy-4-hydroxy-3- quinolinecarboxylic acid, represented by the formula:

RO- COOR2 R10- \N/ wherein R and R each represent a member of the group consisting of a lower alkyl radical containing from two to four carbon atoms and R represents a lower alkyl group.

These new compounds are distinguished by the high order of chemo-therapeutic activity which they exhibit in the treatment of parasitic infections in animals when administered in far less than toxic amounts. They have proved surprisingly successful upon oral administration in combatting coccidiosis.

Coccidiosis, a prevalent and economically signficant disease of poultry, is caused by a variety of coccidia including El'meria terzella, Eimeria acervu'lina and Eimerz'a necatlix. The new compounds of this invention are highly effective agents against such coccidia. When incorporated in a nutritionally balanced diet at a level of from about 0.006 to about 0.1% by weight and offered to coccidially infected chickens, they overcome the mortality and morbidity usually associated with coccidial disease and accomplish a salutary elfect upon growth and appearance of the birds.

The preparation of these new compounds in a form permitting convenient administration is readily accomplished by admixing them in the diet of animals as indicated hereinabove. They may, if desired, be incorporated in tablets, gelatin capsules, suspensions or like compositions consisting of suitable carriers and adjuvants common to the pharmaceutical art.

The method which is currently preferred for the preparation of the new compounds of this invention consists in reducing a 1,2-dialkoxy-4-nitrobenzene in the presence of a catalyst such as palladium-on-carbon and a solvent such as ethanol; addition of the appropriate dialkylalkoxymethylene malonic ester; for instance, diethylethoxymethylene or dimethylmethoxymethylene malonate, to the solution of the reduced product; removal of the solvent; and addition of a temperature regulating medium such as Dowtherm followed by application of heat to the mixture.

Other lower alkyl esters may be prepared by the saponification of one of them followed by subjecting the acid formed to the Fisher-Speier or Schotten-Baumann reaction. Still another method for preparing various lower alkyl esters consists in the trans-esterification technique whereby one alcohol moiety is exchanged for another.

In order that this invention may be fully available to and understood by those skilled in the art, the following examples for preparing the compounds thereof are described briefly:

EXAMPLE I Ethyl 6,7-dieth0xy-4-hydr0xy-3-quinolinecarboxylafe 1,2-diethoxy-4-nitrobenzene (30 g., 0.142 mole) is placed in a heavy-walled bottle with 3 g. of 5% Pd-oncarbon and ml. of ethanol. In 1 hour 38.5 p.s.i.g. of hydrogen is absorbed (theory 36.2). The catalyst is filtered off and washed with a small amount of ethanol.

In a 1 liter, 3-necked flask is placed the above alcoholic solution and 30 g. (0.142 mole) of diethylethoxymethylene malonate is added. Nitrogen is bubbled through the mixture, which is heated on the stream bath to distill off ethanol. After this, 300 ml. of Dowtherm A is added and the temperature rapidly raised to 250 C. by heating with a mantle. The mixture is allowed to reflux for 30-40 minutes and the solution is then allowed to cool. The crystals that form are filtered and washed with hexane. There are obtained 18.6 g. (61% yield); M.P. 275-280 C.; of ethyl 6,7-diethoxy-4-hydroxy-3-quinolinecarboxylate.

Calc. for C H NO C, 62.94; H, 6.27; N, 4.59. Found: C, 62.68; H, 6.25; N, 4.94.

EXAMPLE II Ethyl 6,7-dibut0xy-4-hydr0xy-3-quil10linecarboxylate In .a heavy-walled bottle is placed 29.48 g. (0.11 mole) of 1,2-dibutoxy-4-nitrobenzene, 200 ml. of ethanol and 3 g. of Pd-on-carbon. Theoretical uptake of hydrogen upon reduction of this mixture in a Parr apparatus is achieved in one hour (30 p.s.i.g.). The reduction is repeated with an equal amount of the nitro compound. The reduced material is combined, filtered and the catalyst washed with ethanol. The filtrate is placed in a 1 liter, 3-necked flask together with 47.5 g. of diethylethoxymethylene malonate. The mixture is heated on a steam bath and ethanol removed by distillation. Dowtherm A (600 ml.) is added and the mixture is rapidly heated to reflux (250 C.). After refluxing for 40 minutes, the mixture is cooled to room temperature. Hexane is added. The crystalline precipitate is filtered and. washed with hexane. A 29% yield of crude ethyl 6,7-dibutoxy-4- hydroxy-3-quinolinecarboxylate is obtained (22.76 g.) (M.P. 260-285 C.).

This may be recrystallized from dimethylformamide using charcoal, if desired, to yield 19% of ethyl 6,7-dibutoxy-4-hydroxy-3-quinolinecarboxylate having a melting point of 279-284 C.

Calc. for C H NO C, 66.46; H, 7.53; N, 3.87. Found: C, 66.36; H, 7.42; N, 3.70.

EXAMPLE III Ethyl 6,7-dipr0p0xy-4-hydroxy-S-quinolinecarboxylate In a heavy-walled bottle is placed 38 g. (0.16 mole) of 1,2-dipropoxy-4-nitrobenzene, 200 m1. of ethanol and 3 g. of 5% Pd-on-carbon. The mixture is hydrogenated in a Parr apparatus to give a hydrogen uptake of 41 p.s.i.g. (theory 42 p.s.i.g.). This is repeated until a total of 172 g. (0.72 mole) of nitro compound has been reduced.

The catalyst is filtered off and the ethanolic filtrates are a hexane. The yield of title compound is 96 g. (40% yield from the nitro compound). It may be recrystallized from dimethylformamide (M.P. 27l273 C.).

Calc. for C H NO C, 64.85; H, 6.95; N, 4.20. Found: C, 64.70; H, 6.80; N, 4.43.

EXAMPLE IV Methyl 6,7-diethxy-4-hydroxyquinoline-S-carboxylate A. In a 1 l. flask is placed the ester of Example I, 73 g. (0.24 moles), and 300 ml. of 10% sodium hydroxide solution. The mixture is refluxed for 2 /2 hours. Charcoal is added and the mixture is filtered hot. It is then allowed to cool. The mixture is acidified with about 200 ml. of 1:1 hydrochloric acid (100 ml. conc. hydrochloric acid and 100 ml. of water). A cream-clored precipitate forms. This is filtered, Washed with water and allowed to dry overnight at 110 C. In this way, 6,7-di'ethoxy-4- hydroxyquinoline-3-carboxylic acid is obtained, M.P. 265-273 C. This may be recrystallized from dirnethylformamide to give a melting point of 266269 C. to 56 g. (0.2 mole) of the acid suspended in 1500 ml. of benzene is added 15 ml. (0.2 mole) of thionyl chloride with stirring. The mixture is heated at reflux with stirring for 8%. hours until no more HCl gas is evolved. After slight cooling, the solid is collected and washed well with benzene and then ether, yielding 56 g. (94.7%) of acid chloride, M.P. 260 C.

A suspension of 54.5 g. (0.185 mole) of the acid chloride in 1500 ml. of methanol is heated at reflux on the steam bath for hours. The reaction mixture is filtered hot and the filtrate cooled. The solid which separates is filtered and washed with ether; weight 13 g. On adding water to the original filtrate more solid is obtained which is collected and dried. A total of about 50 g. (93%) of crude product is obtained. Recrystallization from 3 l. of dirnethylformamide and charcoal gives 35.0 g. of methyl 6,7-diethoxy-4-hydroxy-3-quinolinecarboxylate melting at 276.5-278.5 C.

Calc. for C H NO C, 61.80; H, 5.83; N, 4.81.

, Found: C, 61.64; H, 5.93; N, 4.95.

EXAMPLE V Ethyl 6,7-diisopropoxy-4-hydr0xy-3-quin0lihecarb0xylate A. o-DIISOPROPOXYBENZENE A slow stream of nitrogen is passed through a solution of 220 g. (2 moles) of catechol in 900 ml. of alcohol in a 3 l. 3-necked flask equipped with stirrer, reflux condenser, dropping funnel and nitrogen inlet. After a few minutes stirring, 160 g. (4 moles) of sodium hydroxide is added and stirring is continued until practically all of the sodium hydroxide has dissolved. To the stirred, thick suspension is added 750 g. (6 moles) of 2-bromopropane over a 2-hr. period, maintaining gentle refluxing by means of a steam bath. After the addition, the nitrogen is turned off and refluxing is continued for 18 hours. The mixture is cooled thoroughly and the sodium bromide is filtered and washed with alcohol. The combined filtrate and washings are concentrated in vacuo until as much alcohol as possible has been removed. A further amount of sodium bromide which separates during the concentration is removed; a total of 390 g. of sodium bromide (95% of calcd.) was obtained.

The oily residue is dissolved in 500 ml. of ether and extracted with four 200 ml. portions of 10% sodium hydroxide solution, then with two 100 ml. portions of water.

The ether solution is dried over magnesium sulfate and concentrated, first at atmospheric pressure and then in vacuo, to an amber-colored oil weighing 182 g. (47% of theory for diisopropoxybenzene).

the dark, oily product extracted with three 250 ml.

portions of chloroform. The combined choroform extracts are washed with three 100 ml. portions of water and dried over magnesium sulfate. An equal volume of carbontetrachloride is added and this solution is poured onto a 60 x 600 mm. column of alumina (Merck 71707; ca. 3.5 lbs.). The column is eluted with a mixture of equal parts of chloroform and carbon tetrachloride at a flow rate of 30 ml./min. After collection of ca. 3 l. of yellow solution, the eluate became almost colorless, a dark brown zone remaining at the top. Concentration of the yellow eluate in vacuo gives 100 g. (58%) of the titled nitro compound as a yellow oil.

C. ETHYL 6,7-DIISOPROPOXY-4-HYDROXY-3- QUINOLINECARBOXYLATE A 20 g. portion (0.084 mole) of 1,2-diisopropoxy-4- nitrobenzene is hydrogenated over 2 g. of 10% palladiumcharcoal catalyst in 200 ml. of alcohol at 40 p.s.i. initial pressure. The reduction ceases after a pressure drop of 23 lbs. (87% of calcd.) in 30 min. The catalyst is filtered, 18 g. (0.084 mole) of diethylethoxymethylene malonate is added and the solution is heated under reflux for 2 hours. The amber-colored, oily residue remaining after distillation of the alcohol in vacuo is added to 900 ml. of Dowtherm A at ca. 245 C. This solution is boiled for 30 min, then allowed to cool overnight. The crude product is filtered, washed with Dowtherm, then with benzene and 'dried at C.; 9.7 g. (35%) of the title compound is obtained as light tan crystals, M.P. 220-228 C. Recrystallization from dimethylformamide gives 6.4 g. of white crystals, M.P. 233-234" C.

Calc. for C H NO C, 64.85; H, 6.95; N, 4.20.

Found: C, 64.53; H, 6.94; N, 4.37.

EXAMPLE VI Methyl 6,7-diis0pr0p0xy-4-hydr0xy-3- quinolinecarboxylate A 25 g. sample (0.11 mole) of 1,2-diisopropoxy-4- nitrobenzene (Example V, B) is hydrogenated over 4 g. of 5% palladium-charcoal catalyst containing 50% water in 200 ml. of alcohol at 40 p.s.i. initial pressure. The reaction ceases after a pressure drop of 23 lbs. (87% of calcd.) in 30 min. The catalyst is filtered and to the combined filtrates from two such reductions is added 38 g. (0.22 mole) of dirnethylmethoxymethylene malonate in 200 ml. of alcohol. This solution is heated under reflux for 1% hours and then concentrated in vacuo to a viscous residue.

This residue is heated on a steam bath and added to 1400 ml. of Dowtherm A preheated to 245 C. The solution is boiled for 20 minutes; then allowed tocool. The crude product is filtered, washed with Dowtherm, then with acetone and air dried; 25 g. (40%) of the title compound is obtained, M.P. 244-252 C.

Recrystallization of 52 g. of this product from 550 ml. of dimethylformarnide gives 43 g. of white crystals, M.P. 253-256 C.

Calc. for C H NO C, 63.93; H, 6.63; N, 4.39. Found: C, 64.03; H, 6.52; N, 4.53.

EXAMPLE VII Ethyl 6,7-diis0but0xy-4-hydr0xy-3-quin0linecarb0xylate To a solution of 197 g. (1.8 M) of catechol in 730 ml. of ethanol is added 143 g. (3.6 M) of sodium hydroxide pellets in a nitrogen atmosphere. When salt formation is complete, 490 g. (3.6 M) of isobutyl bromide is added dropwise at 5565. The nitrogen inlet tube is removed, and this mixture is refluxed for 17 hours. The sodium bromide is removed by filtration and the filtrate concentrated. The tar-like residue is taken up in 2 1. of water and extracted with 2 l. and then 1 l. of ether. These ether extracts are combined and Washed with 2 500 ml. of a sodium hydroxide solution and then with 2X1 1. of H 0. After drying the ether solution over MgSO it is concentrated to a residue weighing 125 g. (33%).

While maintaining the temperature below 25 with an ice bath, 105 g. (.47 M) of 1,2-diisobutoxybenzene is added dropwise to a 1:1 solution of water and concentrated nitric acid. On completion of the addition, cooling is continued until the reaction is no longer exothermic, The mixture is poured into 2 1. of ice water with stirring. The resulting brown solid is filtered, washed well With water until washings are no longer acid, dissolved in slightly warm methanol and filtered. A little water is added to induce crystallization. The recrystallized material weighs 49 g. (39%), M.P. 68-72 C.

To 2 g. of 5% Pd/O containing 50% water is added 16 g. (.06 M) of 3,4-diisobutoxynitrobenzene and 200 ml. of ethanol. On shaking in a hydrogen atmosphere for 20 minutes the theoretical amount of hydrogen is consumed. The catalyst is removed by filtration, and the filtrate is added to 13 g. (.06 M) of diethylethoxymethylene malonate and refluxed in a nitrogen atmosphere for 1 hour. White crystals of the anil separate upon cooling to room temperature, 18 g. (74%), M.P. 77-79 C.

A 56 g. sample of the anil prepared in this Way is added to 600 ml. of Dowtherm and the solution refluxed for 1 hour. The solid product is washed with hexane, giving 31 g. (81%), M.P. 282-284 C. Two recrystallizations from dimethylformamide yield g. of title product M.P. 288-291" C.

Calc. for C2 H2qNO5: C, 66.46; H, 7.53; N, 3.87. Found: C, 66.53; H, 7.24; N, 4.13.

EXAMPLE VIII ample VI and 20 g. of p-toluene-sulfonic acid in 1600 ml. of isopropanol is heated to reflux for 70 hours. The solution is filtered and the filtrate cooled. A small amount of solid separates and is discarded. The filtrate is concentrated on the steam bath at reduced pressure. The solid residue is collected and washed with ether and dried. It is then triturated with Na CO solution and collected and washed well with H O. Recrystallization from about 800 ml. isopropanol gives 26.7 g. of title product (38.5%) M.P. 225-228 C.

Calc. for C H NO C, 65.69; H, 7.25; N, 4.03. Found: C, 65.30; H, 7.40; N, 3.90.

What is claimed is:

1. A lower alkyl ester of a 6,7-di(lower) alkoxy-4-hydroxy-3-quinolinecarboxylic acid of the formula:

R0 OOORz RIO \N/ wherein R and R each represent a member of the group consisting of a lower alkyl radical containing from two to four carbon atoms, and R represents a lower alkyl group.

2. Ethyl 6,7-diethoxy-4-hydroxy 3 QUlIIOIlIIB-CEUI'bJOX- ylate.

3. Ethyl 6,7-diisopropoxy 4 hydroxy 3 quinolinecarboxylate.

4. Ethyl 6,7-dipropoxy 4 hydroxy 3 quinolinecarboxylate.

5. Methyl 6,7-diethoxy 4 hydroxy 3 quinolinecarboxylate.

6. Methyl 6,7-diisopropoxy 4 hydroxy-3-quinolinecarboxylate.

7. Ethyl 6,7-dibutoxy 4 hydroxy 3 quinoline-carboxylate.

8. Ethyl 6,7-diisobutoxy 4 hydroxy 3 quinolinecarboxylate.

9. Isopropyl 4-hydroxy-6,7-diisopropoxy -3- quinolinecarboxylate.

References Cited by the Examiner Riegel et al., J. Am. Chem. Soc., vol. 68, pp. 1264-66 (1946).

Takahashi et al, Chem. Abstracts, vol. 47, col. 6947 (1953).

HENRY R. J ILES, Acting Primary Examiner. DONALD G. DAUS, Assistant Examiner, 

1. A LOWER ALKYL ESTER OF A 6,7-DI(LOWER) ALKOXY-4-HYDROXY-3-QUINOLINECARBOXYLIC ACID OF THE FORMULA: 